The subject matter of the present invention relates to a workstation based software method and apparatus, which is responsive to received seismic data and well log data, for generating a grid composed of a plurality of individual cells which is imposed upon each horizon of an earth formation and further generating a corresponding plurality of "more accurate" information relating, for example, to the transmissibility properties of the plurality of cells of the grid, the plurality of "more accurate" information being input to a conventional simulator which generates a corresponding plurality of simulation results (such as pressures and saturations) pertaining, respectively, to the plurality of cells of the grid, the plurality of simulation results being overlayed, respectively, upon the plurality of cells of the grid so that a new simulation result is associated with each cell of the grid, the cells of the grid and the new simulation results associated therewith being displayed on the workstation display monitor for viewing by an operator of the workstation.
Seismic operations are performed near one or more wellbores in an earth formation, and a plurality of seismic data is obtained from such seismic operation. In addition, well logging operations are also performed in the one or more wellbores and well log data is also obtained from the well logging operations. The seismic data and the well log data is input to a computer workstation where an interpretation program is executing. The interpretation program of the prior art was comprised of a first program sometimes called "grid" which generated data, and a second simulation program, responsive to the first program, which received the data from the first "grid" program and generated a set of simulation results and displayed the simulation results on the workstation display, the displayed simulation results enabling an operator to determine the flow properties of the earth formation situated near the one or more wellbores drilled into the formation. In particular, the first "grid" program establishes a grid for each horizon in the earth formation near the wellbores, the grid for each horizon comprising a multitude of individual cells. In addition, the first "grid" program generates data and other information for each of the individual cells for each horizon, the data and other information for each cell being transmitted to the second simulation program which uses the data and information received from the first program to generate a set of simulation results for each cell of the grid, a simulation result being displayed on the workstation display for each cell of the grid thereby enabling an operator of the workstation to determine the flow producing properties of each of the cells in the gridded earth formation located near the wellbores drilled into the formation.
However, continuous developmental efforts are focused on improving the quality and accuracy of the data and other information generated by the first "grid" program. When a set of improved and more accurate data is received by the second simulation program, the simulation function practiced by the second simulation program will be more accurate and complete; that is, the simulation results generated by the second simulation program will be more accurate and complete. Consequently, in view of the more accurate and complete set of simulation results generated by the second simulation program, the flow properties associated with each cell of the earth formation located near the wellbores can be more accurately determined.
Consequently, a need exists for improving the first program of the interpretation program such that more accurate data is generated by the first program. More particularly, since the data generated by the first program of the interpretation program includes a parameter known as "transmissibility" which relates to the transmissibility or flow properties of each cell of the grid imposed on the formation, a need exists for improving the first program of the interpretation program executing in the workstation so that more accurate "transmissibility" data is generated by the first program.
When more accurate transmissibility data is generated by the first program, more accurate simulation results can be generated by the second simulation program of the interpretation program. As a result, in response to the more accurate simulation results, a display on said workstation will display more accurate data, such as pressures and saturations, associated with each cell of the grid of the earth formation near the wellbores. Consequently, the flow properties of the formation near the wellbores are more accurated determined.
More particularly, flow simulations on grids based on triangles have been used by various authors inside and outside the petroleum industry. Winslow.sup.24 used control volumes formed around each node of a triangular grid by joining the edge midpoints to the triangle centroids for solving a 2D magnetostatic problem. This technique was applied to reservoir simulation by Forsyth.sup.12, and is commonly known as the control volume finite element (CVFE) method. Cottrell et al..sup.9 used control volumes formed by joining the perpendicular bisectors of triangle edges of a Delaunay.sup.10 triangulation for solving semiconductor device equations. Heinemann et al..sup.18 applied this technique to reservoir simulation, which is known as the PEBI or the Voronoi.sup.23 method. Further work on the CVFE method was presented by Fung.sup.13 and on the PEBI method by Palagi.sup.19 and Gunasekera.sup.15. Both Forsyth and Fung handled heterogeneous problems by defining permeability to be constant over a triangle. Aavatsmark.sup.1 and Verma.sup.22 derived an alternative difference scheme based on the CVFE method in which permeabilities are defined to be constant within control volumes. This approach handles boundaries of layers with large permeability differences better than the traditional CVFE method and as with the traditional method it leads to a multi-point flow stencil, hence referred to as an MPFA scheme. By contrast, the PEBI method reduces to a two point flow stencil. Heinemann et al..sup.18 and Amado et al..sup.4 extended the PEBI method to handle anisotropic heterogeneous systems by defining permeability to be constant within a triangle and by adjusting the angle between triangle edges and cell boundaries. This approach has two problems; firstly handling layers of contrasting permeabilities is poor, secondly in highly anisotropic systems the angle condition between triangle edges and cell boundaries may become so severe that cells begin to overlap, as shown in Verma.sup.22. As an alternative to using control volumes formed around nodes of triangulations it is possible to use the triangles themselves as control volumes. Examples of such schemes are Aavatsmark.sup.1, Durlofsky.sup.11, Cominelli et al..sup.8 and Gunasekera.sup.16. A drawback of triangular control volumes compared to Voronoi volumes is the much higher number of cells in the former; for random point distributions an average factor of two and five exist in two and three dimensions respectively. An advantage of triangular grids is the flexibility in honouring complex geological and production features.